In Release 10 of long term evolution (LTE) wireless communication system standards and prior releases, the physical downlink control channels (PDCCH) carry all of the downlink (DL) and uplink (UL) scheduling information to inform individual wireless devices where to find information in the time and frequency resources utilized for transmissions between the wireless devices and a base station, such as an eNodeB (eNB).
Such a typical wireless communication system 10 is shown in FIG. 1. A network node 12, often referred to as a base station, is in communication with a backhaul network 14. The backhaul network 14 may include the Internet and/or the public switched telephone network (PSTN). The network node 12 communicates with a plurality of wireless devices 16a, 16b and 16c, referred to collectively herein as wireless devices 16. Although only one base station 12 is shown, an actual wireless communication system 10 has many base stations. Also, there will typically be more than three wireless devices 16.
In communication systems based on LTE standards, downlink communications between the network node 12 and the wireless devices 16 are based on a basic radio frame an example of which is illustrated in FIG. 2. A basic radio frame generally includes 20 slots which are paired together to form subframes. With additional reference to FIG. 3, each slot of the basic radio frame generally includes multiple resource elements (REs) which can be illustrated as a resource grid including multiple frequency carriers and multiple orthogonal frequency division multiplexing (OFDM) symbols. In the resource grid, one RE denotes a single OFDM symbol transmitted over a single frequency carrier. As illustrated in FIG. 3, OFDM symbols and frequency carriers can be grouped as resource blocks (RBs). An LTE RB generally includes 7 OFDM symbols over 12 frequency carriers for a total of 84 REs per RB. However, these quantities can vary.
When two slots are combined into a subframe, as shown in FIG. 2, their combined resource elements are further divided into a control region which generally occupies the first 3 OFDM symbols (the first 4 OFDM symbols when the available bandwidth is 1.4 MHz) over the available bandwidth, i.e. over all the available frequency carriers, and a data region which occupy the remaining OFDM symbols, also over the available bandwidth. In FIG. 4, which illustrates an exemplary subframe, the shaded region is the control region while the non-shaded region is the data region.
The network node 12 generates and transmits a PDCCH which informs each wireless device 16 whether and when data is to be transmitted to the wireless device 16 or received from the wireless device 16. According to the aforementioned communication standards, a wireless device 16 must decode the PDCCH successfully in order to receive and send data. The PDCCH is located within the control region of a subframe which, as indicated above, usually occupies the first 3 OFDM symbols at the beginning of each transmitted subframe.
The capacity of the PDCCH is a limiting factor in systems where there are a large number of wireless devices using low rate services such as voice over Internet protocol (VoIP). Indeed, due to the limited size of the control region, the number of PDCCHs than can be transmitted in any given subframe is limited. To alleviate the limitations of the control region, Release 11 of the LTE communication standards introduces an enhanced PDCCH (ePDCCH) that employs frequency division multiplexing (FDM) and that can be allocated dynamically within the data region of a subframe in which the data are transmitted over physical downlink shared channels (PDSCH).
The introduction of the ePDCCH poses challenges to achieving power efficiency in a wireless device. Modern wireless device receivers employ “micro-sleep” techniques to conserve battery power. These techniques allow the wireless device to power down its radio frequency (RF) components when the wireless device does not expect to receive and decode any data in a frame. The wireless device employs fast decoding of the PDCCH to determine if the wireless device is scheduled to receive and decode data during the frame. If not, the wireless device stops buffering data of the PDSCH transmitted in the data region and sleeps during the remainder of the sub frame.
However, these micro-sleep techniques are not possible when the ePDCCH is used because the ePDCCH is distributed in the data region over the entire duration of the subframe, forcing the wireless device to remain awake and monitor the entire subframe for the ePDCCH before it can decode the scheduling data contained in the ePDCCH.
Thus, a wireless device that is assigned an ePDCCH channel will experience increased power consumption and increased processing load as compared with communication techniques that do not employ ePDCCH, because the wireless device must decode the ePDCCH that spans over the entire frame duration.